The conventionally available bladders in the market either posses low air permeability property or have the high bounce property. There is always a need for the bladders which are having both the low air permeability and high bounce properties.
In the rubber bladders as known conventionally, rubber compounds such as butyl rubber are compounded on a rubber mill or banbury mixer. This compound is then calendered to the desired thickness in sheet form. From the rubber sheet, quarter sections of the bladder are die cut and pieced together by hand with adhesive and end patches. A valve is inserted and adhered to the construction. The total construction is then heat cured to produce a bladder. The adhesive application results in the imperfect seals and poor weight balance. This conventional process often results in high amounts of defective bladders and excess scrap.
The bladders made up of thermoplastic materials such as polyethylene powders and vinyl plastisols are also known conventionally. However, these materials are found to have no bounce but have good air retention and hence found not suitable for inflatable bladders.
The inflatable bladders made up of natural rubber are also available conventionally. The latex rubber bladder shell made from natural rubber latex as available in the market are found to have very good bounce property but have high air permeability properties. Due to high air permeability, the air leaks out frequently leading to frequent refilling of the bladder within short durations.
The bladders made up of butyl rubber are also known conventionally. The bladder composition containing low unsaturated butyl rubber has been disclosed in U.S. Pat. No. 4,022,848. This Patent teaches the use of butyl rubber composition in tire curing bladders, air bags and curing tubes.
Butyl rubber is well known in the art and is disclosed in U.S. Pat. No. 3,031,423, column 1, lines 15 to 24. The problems faced with the butyl rubber bladder is that while it has a good air retention, but it lacks in good bounce properties.
Hence, there is a need to decrease the air permeability without affecting the bounce and other properties.